The present invention relates generally to the field of transistor mounting devices, and more particularly to a device for mounting a plurality of transistors to a heat sink mounted which forms part of a machine control motor.
It has long been well known to utilize stepper motors, sometimes referred to as "smart" motors, to control various mechanical functions of complex machines. A principal advantage of utilizing such motors is that they can be very precisely controlled with respect to direction, speed, acceleration and deceleration, and degree of rotation of the motor rotor with respect to each intermittent movement of the rotor. Typically a machine will utilize many such motors to drive various mechanical assemblies in the machine, such as, an envelope feeder, a printer system, a tape feeder, etc. The operation of the motors is controlled from a central microprocessor which determines the sequence and mode of operation of the motors in accordance with any desired predetermined pattern to cause the mechanical functions of the machine to occur in a precise predetermined order.
Typically, the operation of each individual motor is controlled by a series of transistors which function to energize and deenergize the electrical circuitry to the banks or phases of the motor. For example, in a three phase motor there are three coils inside the rotor, and as each coil is activated by a respective transistor, which simply switch to the respective coils off and on. The rotor then turns to align the magnets of the rotor with the stator coils, thereby providing very precise positioning of the rotor and any mechanical part which is driven by the rotor. In addition, the motor is often provided with an optical encoder which monitors the operation of the motor to ensure that the rotor has turned in the direction, degree and speed as determined by the microprocessor.
In the normal course of operation, the transistors generate a considerable amount of heat and, therefore, must be mounted on a suitable heat sink associated with the motor to dissipate the heat that would otherwise cause the transistors to fail, thereby rendering the motor inoperable for its intended purpose.
Prior to the present invention, the normal procedure for mounting transistors to a heat sink was first to place a lock washer and then a flat washer onto a screw. The screw is then through an aperture in the wall of the heat sink and then through an aperture formed in the mounting tab of the transistor. An individual electrical insulator is then placed on the screw followed by a nut. The nut is then tightened on the screw to hold the transistor securely on the wall of the heat sink. This procedure required five individual parts to secure each transistor to the wall of the heat sink. Since six transistors are required to control the operation of a three phase motor, 30 individual parts are required to secure the six transistors to the heat sink for each motor in the machine, of which there are several. Thus, it is apparent that with a machine having ten motors, as many machines do, 300 individual parts are required just to mount the motor controlling transistors to the heat sinks.
In addition to the number of parts required and the cost thereof, a considerable amount of time is expended in the labor required to assemble these parts. For each transistor, an assembly person must handle and assemble five parts, not including the transistor and a heat transfer pad which is inserted between the transistor and the wall of the heat sink. Again, for each motor, the assembly person must handle and assemble 30 parts, or 300 for a machine having 10 motors. The amount of time required for all of this assembly work is a significant contribution of the overall cost of the manufacture of the machine.